The present invention relates generally to the design and synthesis of polymers and macromolecules. In particular, the present invention relates to new class of multiple branched, functional polyethylene glycols. The inventive multiple-branched, functional polyethylene glycols are synthesized by a series of chemical reactions involving linear polyethylene glycols and small molecules to obtain the inventive multiple-branched, functional polyethylene glycols.
There are various types of pharmaceutical drugs, including anti-tumor drugs, which can be classified generally into two categories based on their molecular weights: Type I drugs and Type II drugs. Type I drugs are smaller molecules with relatively lower molecular weights typically less than or equal to about 1 kDa. Most Type I drugs are chemically synthesized or are the result of laborious extraction and purification from naturally occurring sources. Examples of Type I drugs are nitrogen mustards, cis-platinum, 5-fluorouracil, paclitaxel and the like. Type II drugs are macromolecular drugs, most of which are genetically engineered recombinant proteins or peptides. Both Type I and Type II drugs suffer from higher toxicity rates, poor solubility, and relatively lower half life. Furthermore, most proteins and peptides drugs are immunogenic, which may induce harmful immunoreactions.
One of the methods to resolve these problems is through the chemical modification of the drugs with polymers. Caliceti, T. et al., J. Bioactive Compatible Polym. 10:103–120 (1995) disclose modification of superoxide dismutase with polyvinyl pyrrolidone. Uren, J. R. et al., Cancer Res. V39, 1927–1933, 1981) discloses modification of L-asparaginase with polyDL-alanine. One of the most popular methods of chemically modifying drugs is to use activated polyethylene glycol (PEG) as a drug matrix. For example, Nandini, K et al., European Granted Patent No. EP0247860B2, published Jul. 8, 1992 and Clark, M. A., et al, PCT International Publication No. WO 98/31383 published Jul. 23, 1998, 1998 (PCT/US98/00683) describes the reaction of tumor necrosis factor (TNF) with PEG; Gilbert, C. W et al. U.S. Pat. Nos. 5,951,974, 5,981,709, and 6,042,822 teach using PEG to chemically modify interferon-α. Similar reactions such as modification of interleukin-2 with PEG, Prakash, R. K. et al. U.S. Pat. No. 6,251,866, and PEG modification of granulocyte-macrophage colony-stimulating factor (GM-CSF) with PEG, Knusli, C. et al. Br. J. Haematl, 82 (4), 654–663 (1992); Malik, F et al. Exp. Hemaol, 20(8), 1028–1035(1992), One of ordinary skill in the art will understand that PEG modification of growth hormones is well known. Each of the foregoing references are hereby incorporated by reference as generally teaching that it is known to PEGylate pharmacologically active agents.
Commonly used active groups in PEG modification of pharmaceuticals, include succinimide active esters, aldehyde group, trifluorsulfonate, p-nitrophenylcarbonate, benzotriazole carbonate etc. Commonly used PEG molecules are either linear or branched monomethoxypoly ethylene glycols with molecular weights ranging from 2–60 kDa, See, e.g., Monfardini, C. et al. Bioconjugate Chem. 6:62–69 (1995).
The properties of pharmaceuticals modified by polymers typically depend on a number of factors, including, structure, molecular weight, molecular weight distribution, and configuration of polymer materials used. Therefore, the properties of a PEG-modified drug with the same structure, but with different molecular weights will be different. Furthermore, differences in resulting properties will exist among PEG-modified drugs which have the same structure and molecular weight, but differ in the configuration of the PEG polymers employed. Difficulties have been encountered in PEG-modification of proteins and other pharmaceuticals. Among these difficulties is a lack of conjugating selectivity, which leads to conjugation at active sites of the proteins. This results in a reduction of the bioactivity of the of the drug or protein. Another difficulty is site specific conjugation. For example, some proteins have multiple sites that are susceptible to PEG-modification, which makes site specific PEG modification on such proteins quite difficult. Consequently, quality control is quite difficult for these types of pharmaceutical conjugates.